Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation

Abstract

The inclusion of more sustainable alternatives such as bacterial inoculants is a viable option for the competitiveness of vegetable crops in tropical countries such as Colombia. The economic feasibility of a bacterial suspension of G. diazotrophicus applied to the carrot crop was determined. The native isolate G. diazotrophicus GIBI029 was evaluated and the strain ATCC 49037 was used as a control. The experiment was installed in a subdivided plot design, where the plot was the bacterium G. diazotrophicus (ATCC49037 and GIBI029. The subplot was the concentration of G. diazotrophicus (88×10⁶ CFU/mL and 18×10⁷ CFU/mL) and, in it, the levels of nitrogen and phosphorus (0% and 100% nitrogen and phosphorus) were assorted. The average weight of the carrot (g) and the yield by quality of the consuming organ (kg/ha) were evaluated. Through the production cycle, fixed, variable, and total costs were calculated. Benefit / cost ratios higher than 1.46 and net income up to US$ 10,817/ha were achieved. It is possible to efficiently and economically use the native isolate G. diazotrophicus GIBI029 in the search for more sustainable and competitive cultural practices.
Keywords:
diazotrophic bacteria; plant growth promoter; benefit / cost ratio

Full text

40 Nelson Ceballos-Aguirre et al.
Rev. Ceres, Viçosa, v. 69, n.1, p. 040-047, jan/feb, 2022
ABSTRACT
Submitted on December 2nd, 2020 and accepted on June 25th, 2021.
1 Departamento de Producción Agropecuaria, Universidad de Caldas, Manizales, Caldas, Colombia. nelson.ceballos@ucaldas.edu.co
2 Instituto de Investigación en Microbiología y Biotecnología, Universidad Católica de Manizales, Manizales, Caldas, Colombia. grestrepo@ucm.edu.co
3 Departamento de Agronomía, Universidad de Pamplona, Pamplona, Norte de Santander, Colombia. alhuza@gmail.com
4 Departamento de Ciencias Biológicas, Universidad Autónoma de Manizales, Manizales, Caldas, Colombia. jorgeacuellarg@autonoma.edu.co
5 Departamento de Ingenierías, Universidad de Caldas, Manizales, Caldas, Colombia. osanchez@ucaldas.edu.co
*Corresponding author: nelson.ceballos@ucaldas.edu.co
Economic feasibility of Gluconacetobacter diazotrophicus
in carrot cultivation
The inclusion of more sustainable alternatives such as bacterial inoculants is a viable option for the competitiveness
of vegetable crops in tropical countries such as Colombia. The economic feasibility of a bacterial suspension of G.
diazotrophicus applied to the carrot crop was determined. The native isolate G. diazotrophicus GIBI029 was evaluated
and the strain ATCC 49037 was used as a control. The experiment was installed in a subdivided plot design, where the
plot was the bacterium G. diazotrophicus (ATCC49037 and GIBI029. The subplot was the concentration of G. diazotrophicus
(88×106 CFU/mL and 18×107 CFU/mL) and, in it, the levels of nitrogen and phosphorus (0% and 100% nitrogen and
phosphorus) were assorted. The average weight of the carrot (g) and the yield by quality of the consuming organ (kg/
ha) were evaluated. Through the production cycle, fixed, variable, and total costs were calculated. Benefit / cost ratios
higher than 1.46 and net income up to US$ 10,817/ha were achieved. It is possible to efficiently and economically use the
native isolate G. diazotrophicus GIBI029 in the search for more sustainable and competitive cultural practices.
Keywords: diazotrophic bacteria; plant growth promoter; benefit / cost ratio.
Nelson Ceballos-Aguirre1*, Gloria María Restrepo2, Alejandro Hurtado-Salazar3,
Jorge Andrés Cuellar4, Óscar Julián Sánchez5
10.1590/0034-737X202269010006
This is an open access
article under the CC BY
license Creative Commons
INTRODUCTION
The carrot is one of the most consumed vegetables
worldwide. The world production of carrots reached
39,996,287 t in 2018, corresponding to a total cultivated
area of 1,131,049 ha (Faostat, 2020). Carrot production in
Colombia is very expensive due to the high price of
fertilizers: approximately 25% of the total costs are destined
to the nutrition of the crop.
In the case of carrot cultivation, the Colombian farmer
cannot compete with foreign producers, since imports of
this vegetable present reduced purchase charges and have
low product distribution tariffs. In general, the Colombian
agricultural sector is unaware of the use of new, cheaper
fertilization strategies such as the use of biofertilizers,
which could affect the final marketing price.
The development of biofertilizers traditionally focused
on the production of Rhizobium for its application in legu-
me crops, especially soybeans; however, other alternatives
are currently being explored through the development of
inoculants based on autochthonous nitrogen-fixing
bacteria such as those of the genera Herbaspirillum and
Gluconacetobacter.
In particular, the bacterium G. diazotrophicus exhibits
important properties to promote plant growth, as has been
demonstrated by Beneduzi et al. (2013) and in a previous
work (Restrepo et al., 2017). G. diazotrophicus has the
potential to provide the farmer with benefits such as the
production of phytohormones of both auxins and
gibberellins in significant quantities to allow an efficient
and profitable growth system (Figueroa-Viramontes et
al., 2011). Additionally, it has been detected in grass
plants that these microorganisms have the ability to
naturally solubilize micronutrients such as phosphorus,
zinc, iron, potassium, and magnesium (Eshaghi et al.,
2019). This solubilization property is especially important
in the case of phosphorus, since although high amounts

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Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation
Rev. Ceres, Viçosa, v. 69, n.1, p. 040-047, jan/feb, 2022
of phosphorous fertilizers are applied to cultivable soils in
the world, a large part of this micronutrient is fixed or
immobilized in the soil, preventing its assimilation by plants
(Santos et al., 2019; Paredes-Villanueva et al., 2020; Vejan
et al., 2016). Precisely, G. diazotrophicus exhibits a
significant capacity to solubilize phosphates (Restrepo et
al., 2017), which represents an important characteristic for
a wide range of economically important crops.
Evaluations of native isolates of G. diazotrophicus have
been carried out in various crops such as sugar cane
(Ferreira et al., 2019), cassava and papaya (Dibut et al.,
2010), and tomato (Fernández-Delgado et al., 2019), which
have shown a positive effect on growth promotion, making
it possible to reduce the use of chemical fertilizers.
However, no published articles were found in the available
literature on the evaluation of growth promotion by G.
diazotrophicus in carrot crops. Nevertheless, the economic
analysis of the possibility of implementing a technological
package that includes the use of this bacterium for the
fertilization of carrot crops has not been carried out so far.
Consequently, the present investigation aimed at
determining the economic feasibility of using a bacterial
suspension of G. diazotrophicus in promoting carrot
growth.
MATERIALS AND METHODS
Location
This study was carried out at the Tesorito Farm of the
University of Caldas at an altitude of 2,340 masl (5°01’49"N
and -75°26’13" W), annual rainfall of 1,800 mm, relative
humidity of 78%, solar brightness of 1,215 h-light per year,
average temperature of 17.5 °C and sandy loam type of soil
(Universidad de Caldas, 2014).
Microorganism
The native isolate of the bacterium G. diazotrophicus
GIBI029 from sugar cane was evaluated. The standard
strain G. diazotrophicus ATCC 49037 was used as a control
of the experiments. The native bacterial isolate come from
the Microorganisms Collection of the Universidad Católi-
ca de Manizales and are covered by the Permit for the
Collection of Wild Specimens of Biological Diversity
Framework for non-commercial scientific research purposes
No. 1166, issued by the Environmental Authority of
Environmental Licenses of Colombia (ANLA) to the
Universidad de Caldas.
Preparation of G. diazotrophicus cell suspension
The preparation of the inoculum and bacterial
suspension of G. diazotrophicus was carried out using
the modified DYGS (Silva et al., 2016) and LGI-PN (Sadeghi
& Khodakaramian, 2020) media. The media were inoculated
and incubated at 30 ºC under constant shaking at 150 rpm
for 7 days and were evaluated daily until reaching each of
the required bacterial concentrations (88×106 and
18×107 CFU/mL). During this period, the purity, viability,
and concentration of the bacteria were verified through
the technique of Colony Forming Units per milliliter
(Ahmad et al., 2016).
Experimental design
An experimental design of sub-subdivided plots was
used. The largest plot was made up of the bacterium G.
diazotrophicus (ATCC49037 strain and GIBI029 isolate),
and the following bacterial concentrations were arranged
in the subplots: 88×106 CFU/mL and 18×107 CFU/mL
(Restrepo, 2014). In the subplots, the nitrogen and
phosphorus levels were assorted in two combinations: With
and without the joint addition of nitrogen and phosphorus
(0% and 100% of nitrogen and phosphorus). Nitrogen
fertilization consisted of the addition of 200 kg/ha urea
while phosphorous fertilization consisted of the addition
of 1000 mL/ha phosphoric acid. In all cases, 120 kg/ha KCl
and 80 kg/ha MgSO4 were added. The number of replicas
per combination was 4 blocks. The experimental unit was
12.3 m2. In each experimental unit (block) a minimum of 70
carrot plants will be guaranteed. The combinations of the
treatments and their coding are presented in Table 1. The
variables evaluated to know the effect of the application
of G. diazotrophicus in carrot plants were average carrot
weight (in g) and yield (kg/ha), taking into account the
qualities according to the weight reached by the consuming
organ. The quality grades of the carrot crop consumption
organ were defined according to the following classifica-
tion: Extra quality, greater than 120 g; first quality, 90-119 g;
second quality, 70-89 g; third quality, 30-69 g; less than 30 g,
lower quality equivalent to losses) (Szel¹g-Sikora et al., 2019).
In-field establishment of treatments
The establishment and management of the culture was
carried out according to the protocols described by Szelag-
Sikora et al. (2019). Ten days after sowing (days), it was
applied to each experimental unit or plot, with the
corresponding treatment in foliar spray at the inoculated
rate of 200 mL of bacterial suspension according to the
treatments and concentrations described in the experimen-
tal design.
Evaluation of economic feasibility
The economic feasibility was assessed through indivi-
dual calculation applying the feasibility analysis approach
reported by Herrera et al. (2016). The value of the G.
diazotrophicus suspension was estimated at a value of
231 US dollars (US$), corresponding to the commercial
value of a liquid inoculant of the bacterium in one-liter
presentation (ATCC, 2020). Likewise, the costs of the
different types of fertilization according to the established

42 Nelson Ceballos-Aguirre et al.
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treatments were taken into account. To carry out the
economic analysis, the formats adopted by the Corporación
Colombia Internacional and DANE (DANE, 2017) were
taken into account. The average value of carrots was
estimated for the last 10 years (2010-2020) (Corabastos,
2020). The average commercial value was US$ 0.34/kg,
discriminated as follows: extra US$ 0.49/kg, first US$ 0.43/
kg, second US$ 0.26/kg, and third US$ 0.20/kg (Corabastos,
2020). Finally, the following financial indicators were
calculated according to Arbelaez et al. (2016): Gross and
net income, direct, indirect and total production costs, unit
production margin (UPM), and benefit/cost ratio (B/C R).
Analysis of variance and Duncan’s test were performed
considering a p-value < 0.05. For this, the GLM program of
SAS version 9.1 (SAS Institute, Inc., USA) was used.
RESULTS AND DISCUSSION
In the evaluation of the yields, statistically significant
differences (p dH 0.05) were observed between the
different treatments (Tables 1 and 2). In all cases, the
application of the high level of concentration (d2 =18x107
CFU/mL) of the evaluated bacterial suspensions showed
yields higher than 30,345 kg/ha, as in the case of treatment
with the standard ATCC strain with 100 % fertilization (see
treatment ATCC-d2-100NP in Table 1) that was above the
absolute control without the addition of nitrogenous and
phosphorous fertilizers (Control-0NP) and the commercial
control to which was applied 100% of this type of
fertilization (Control-100NP).
For the native isolation at the d2 concentration with or
without the addition of nitrogenous and phosphate
fertilizers, yields not showing statistically significant
differences were obtained compared to that achieved with
the ATCC 49037 strain applied with this same concentration
with 0% fertilization. This latter treatment exhibited the
highest yield of those evaluated in this work (37,867 kg/
ha). With the values reached, the national average carrot
yield (27,170 kg / ha) and the average yield in the department
(administrative division in Colombia equivalent to a
province) of Caldas (14,500 kg/ha) were exceeded for the
year 2017 (Agronet, 2020). These data indicate an added
value of approximately 15,000 kg / ha.
The greatest losses in harvest of the consuming organ
were presented in the treatments with the low level of the
application concentrations of the bacterial suspensions
(d1 = 88×106 CFU/mL) for both strain types (see last column
in Table 1). The treatment that used the native isolate of G.
diazotrophicus at a low concentration without application
of additional fertilization presented the lowest performance
of those evaluated and presented statistically significant
differences (p < 0.05) with respect to the treatment with the
highest value of performance (coded as ATCC-d2-0NP) as
observed in Table 1.
Table 1: Overall yield and distribution of yield by quality grades for Royal Chantenay carrot depending on the type of strain and applied concentration of G. diazotrophicus and the addition or
not of nitrogenous and phosphorous fertilizers
Concentration Fertilization Yield (kg/ha)
(CFU/mL) (%) Global Extra First Second Third
Loss
- 0 0 Control-0NP 28,290ab 2,946bc 16,350a 5,561cd 2,946cd 487a
- 0 100 Control-100NP 27,901ab 2,663bc 10,880abcd 10,728abc 2,739cd 891a
ATCC 49037 18.0×1070ATCC-d2-0NP 37,867a14,967a14.967a 0e 7,484abcd 449a
GIBI029 18.0×1070GIBI-d2-0NP 31,430ab 6,121b 6,121cde 12,243ab 6,121bcde 823a
ATCC 49037 18.0×107100 ATCC-d2-100NP 30,345ab 6,069b 6,069cde 12,138ab 6,069bcde 0b
GIBI029 18.0×107100 GIBI-d2-100NP 31,597ab 6,320b 6,320cde 12,639ab 6,320abc 0b
ATCC 49037 8.8×1070ATCC-d1-0NP 24,199ab 0d 6,069de 13,563a 4,521bcd 1,594a
ATCC 49037 8.8×107100 ATCC-d1-100NP 23,533ab 0d13,208ab 4,403cd 4,403bcd 1,520a
GIBI029 8.8×1070GIBI-d1-0NP 18,316b0d 3,412e 3,412d10,235ab 1,258a
GIBI029 8.8×107100 GIBI-d1-100NP 19,828ab 0d 3,859de 3,859d11,578ab 532a
Observations: Values with different letters in the same column exhibit statistically significant differences (p < 0.05) according to Duncan’s test.
Strain Code

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Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation
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Table 2: Structure of production costs (in US$/ha) of the Royal Chantenay variety of the carrot crop with the application of G. diazotrophicus as growth promoter
Treatment Control-0NP Control-100NP ATCC-d2-0NP GIBI-d2-0NP ATCC-d2-100NP
Concept Total value % share Total value % share Total value % share Total value % share Total value % share
A. Labor (1+2+3+4) 1,296 35.54 1,296 32.71 1,871 42.62 1,553 38.14 1,499 34.59
(1) Land adaptation 241 6.61 241 6.08 440 10.01 365 8.96 352 8.13
Preparation and sowing 241 6.61 241 6.08 327 7.45 271 6.66 262 6.04
Application of the bacteria to the sowing 00.00 00.00 113 2.57 94 2.30 90 2.08
(2) Crop maintenance 407 11.16 407 10.27 552 12.58 458 11.26 443 10.21
Cultivation work 299 8.20 299 7.55 406 9.24 337 8.27 325 7.50
Application of inputs 108 2.96 108 2.73 147 3.34 122 2.99 117 2.71
(3) Harvest 482 13.21 482 12.16 654 14.89 543 13.32 524 12.09
(4) Post-harvest 166 4.56 166 4.19 225 5.13 187 4.59 181 4.17
B. Inputs (5+6+7+8+9+10+11+12+13+14) 1,825 50.07 2,141 54.06 1,995 45.44 1,995 48.99 2,311 53.31
(5) Seed 599 16.44 599 15.13 599 13.65 599 14.72 599 13.83
(6) Amendment 29 0.79 29 0.73 29 0.66 29 0.71 29 0.67
(7) Organic fertilizer 191 5.25 191 4.83 191 4.36 191 4.70 191 4.41
(8) Edaphic fertilizer 292 8.00 608 15.34 292 6.64 292 7.16 608 14.02
(9) G. diazotrophicus suspension 00.00 00.00 231 5.26 231 5.67 231 5.32
(10) Fungicide 41 1.11 41 1.02 00.00 00.00 00.00
(11) Insecticide 18 0.49 18 0.45 00.00 00.00 00.00
(12) Herbicide 30.07 30.07 00.00 00.00 00.00
(13) Package 327 8.96 327 8.25 327 7.44 327 8.02 327 7.53
(14) Bundle 327 8.96 327 8.25 327 7.44 327 8.02 327 7.53
Direct cost (A+B) 3,121 85.62 3,437 86.76 3,866 88.06 3,548 87.12 3,810 87.90
C. Indirect cost (15+16+17) 524 14.38 524 13.24 524 11.94 524 12.88 524 12.10
(15) Rent 229 6.28 229 5.78 229 5.21 229 5.62 229 5.28
(16) Administration 111 3.04 111 2.80 111 2.52 111 2.72 111 2.56
(17) Incidentals 185 5.07 185 4.66 185 4.21 185 4.54 185 4.26
Total (A+B+C) 3,645 100.00 3,961 100.00 4,390 100.00 4,072 100.00 4,335 100.00
Remarks: Coding of the treatments are deciphered in Table 1.

44 Nelson Ceballos-Aguirre et al.
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Continuation of Table 2.
Treatment GIBI-d2-100NP ATCC-d1-0NP ATCC-d1-100NP GIBI-d1-0NP GIBI-d1-100NP
Concept Total value % share Total value % share Total value % share Total value % share Total value % share
A. Labor (1+2+3+4) 1,550 35.34 1,196 32.19 1,163 29.09 905 26.43 980 25.68
(1) Land adaptation 364 8.30 281 7.56 273 6.83 213 6.21 230 6.03
Preparation and sowing 271 6.17 209 5.62 203 5.08 158 4.62 171 4.49
Application of the bacteria to the sowing 93 2.13 72 1.94 70 1.75 55 1.59 59 1.55
(2) Crop maintenance 457 10.43 353 9.50 343 8.59 267 7.80 289 7.58
Cultivation work 336 7.66 259 6.98 252 6.31 196 5.73 212 5.57
Application of inputs 121 2.77 94 2.52 91 2.28 71 2.07 77 2.01
(3) Harvest 541 12.35 418 11.25 406 10.16 316 9.23 342 8.97
(4) Post-harvest 187 4.26 144 3.88 140 3.50 109 3.18 118 3.09
B. Inputs (5+6+7+8+9+10+11+12+13+14) 2,311 52.70 1,995 53.70 2,311 57.80 1,995 58.26 2,311 60.57
(5) Seed 599 13.67 599 16.13 599 14.99 599 17.50 599 15.71
(6) Amendment 29 0.66 29 0.78 29 0.72 29 0.84 29 0.76
(7) Organic fertilizer 191 4.36 191 5.15 191 4.78 191 5.58 191 5.01
(8) Edaphic fertilizer 608 13.86 292 7.85 608 15.20 292 8.52 608 15.93
(9) G. diazotrophicus Suspension 231 5.26 231 6.21 231 5.77 231 6.74 231 6.05
(10) Fungicide 00.00 00.00 00.00 00.00 00.00
(11) Insecticide 00.00 00.00 00.00 00.00 00.00
(12) Herbicide 00.00 00.00 00.00 00.00 00.00
(13) Package 327 7.45 327 8.79 327 8.17 327 9.54 327 8.56
(14) Bundle 327 7.45 327 8.79 327 8.17 327 9.54 327 8.56
Direct cost (A+B) 3,861 88.04 3,191 85.89 3,474 86.89 2,900 84.69 3,291 86.26
C. Indirect cost (15+16+17) 524 11.96 524 14.11 524 13.11 524 15.31 524 13.74
(15) Rent 229 5.22 229 6.16 229 5.72 229 6.68 229 6.00
(16) Administration 111 2.53 111 2.98 111 2.77 111 3.24 111 2.91
(17) Incidentals 185 4.21 185 4.97 185 4.62 185 5.39 185 4.84
Total (A+B+C) 4,385 100.00 3,715 100.00 3,998 100.00 3,424 100.00 3,815 100.00
Remarks: Coding of the treatments are deciphered in Table 1.

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Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation
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In general, the two types of G. diazotrophicus strain in
the highest concentration proved to be more effective
compared to the commercial control (conventional
treatment used by the farmer), which allows the design of
different production alternatives to the conventional ones
by incorporating biotechnological products such as plant-
growth promoting microbial inoculants.
Boskovic-Rakocevic et al. (2012), when evaluating four
doses of nitrogen fertilization (0, 60, 120 and 180 kg/ha)
found that the content of ß-carotene increased with
increasing rates of nitrogen and it was found that it was
statistically significant even at 120 and 180 kg/ha N,
compared to the control and the lowest dose of 60 kg/ha.
The results of this work highlight the importance of the
use of G. diazotrophicus in its highest concentration, which
allowed a synergistic action with the level of fertilization
applied, resulting in positive effects on crop quality and
yield. In this sense, the physical-chemical and biological
characteristics of the soil must be evaluated in order to
guarantee the sustainability of the productive systems, as
evidenced in this study, which used optimal levels of
nitrogen (0.68 %) and phosphorus (89 ppm) in the soil
reported in the laboratory soil analysis at the beginning of
the trial, reaching the best yields in the crop cycle
evaluated. However, it would be difficult to sustain this
type of response over time if a proportion of nutrients
equivalent to the extraction of the crop is not returned to
the soil or growth promotion strategies such as the
application of the bacterium G. diazotrophicus are not used
in the highest concentration evaluated that demonstrated
the best yields even without the addition of nitrogenous
and phosphate sources.
It should be noted that although the initial phosphorus
contents (89 ppm) in the study site are high, due to the
characteristics of the soil thanks to the presence of
allophane clay, there is a high retention of said element,
reducing its availability for the plant. In this regard, the
phosphate solubilization properties tested for G.
diazotrophicus (Restrepo et al., 2017) make possible to
avoid additional applications of phosphate fertilizers while
preserving optimal crop yields and economic feasibility.
Cruz-Tobar et al. (2018), showed that carrots have a
low response to nitrogen, phosphorus, potassium, and
manure in soils where the main rotation crop was potatoes
due to the residual effect of fertilizers applied in high do-
ses to the crop, obtaining a second quality production.
This situation was not observed in this study, despite the
fact that there was a similar rotation. In addition, the use of
100% nitrogen and potassium fertilization allowed those
authors to obtain a mostly first quality crop. Similarly, it
was shown that the use of only G. diazotrophicus without
any addition of nitrogen and phosphorus resulted in the
best carrot weight (126.48 g), obtaining a very good quality
harvest, as long as the nitrogen and phosphorus levels in
the soil are suitable for the cultivation of this vegetable.
Regarding the production costs of the carrot crop
according to the conditions of Caldas in Colombia, an
investment in 115 days equivalent to the crop cycle was
estimated (Table 2). The values are expressed in US dollars
per hectare during the investment period. The inoculations
of the native isolate G. diazotrophicus for the d1
concentration with and without the addition of nitrogenous
and phosphorus fertilization were the ones with the lowest
share of the harvest labor in the total costs with 28.89%
and 30.55 %, respectively (Tables 1 and 2).
The production costs for one hectare in each of the
bacterial inoculates differ until the beginning of the harvest
because both the cultural tasks and the inputs used present
differential costs (fertilization and labor). The main variation
occurred in the labor category, specifically associated with
harvesting tasks, due to the fluctuation of productivity
that was evidenced in each of the evaluated treatments.
Likewise, a fluctuation in inputs is evidenced due to the
cost of the inoculants (Table 2). During the estimation of
the total costs per hectare, the following parameters were
taken into account: labor costs, supplies, and the cost of
bacterial suspensions
The highest production cost (US$ 4,390/ha) correspon-
ded to the use of the standard strain at the d2 concentration
with and without fertilization with nitrogen and phosphorus
(Table 2). In these treatments, the participation of labor
was high in relation to total costs (42.62%) and based on
the yield obtained (37,867 kg/ha) (Tables 1 and 2).
One of the items with the highest share in production
costs for all evaluated treatments (including controls) was
labor, which ranged between 45.65% and 28.89% of total
production costs. Within the item of labor, cultural tasks
are those with the highest participation due to the slope
conditions of the terrain (eH 5%) present in the study area,
which requires that each one of the tasks is done manually.
Finally, the share percentages of bacterial suspensions at
the concentration of 8.8×107 CFU/mL have an upward
behavior in production costs (labor and supplies) and a
downward behavior for the harvest, taking into account
that the latter is concentrated. In turn, the treatments with
this concentration present a lower yield than the controls.
The carrot crop where the strain ATCC 49037 was
applied at the d2 concentration without nitrogenous and
phosphate fertilization presents the best gross revenue
(US$ 15,208/ha), followed by the treatments with
application of the native isolate with and without
nitrogenous and phosphate fertilization, which presented
gross incomes between US$ 10,000 and US$ 10,500 per
hectare, along with the control treatment without
fertilization (Table 3). The treatments that used bacterial
inoculants of G. diazotrophicus at a concentration of

46 Nelson Ceballos-Aguirre et al.
Rev. Ceres, Viçosa, v. 69, n.1, p. 040-047, jan/feb, 2022
8.8×107 CFU/mL, regardless of whether or not they have
nitrogenous and phosphate fertilization, are the ones with
the lowest yield and, consequently, those that exhibit the
lowest gross income, making them financially unattractive.
The lowest unit production margin (0.12 U$/kg) was
obtained for the treatment with the strain ATCC 49037
applied at the high level of concentration (18×107 CFU /
mL) without fertilization, while the UPM of the commercial
control (farmer’s conventional treatment with 100%
fertilization) was US$ 0.14/kg. This constitutes a
competitive advantage for the farmer who decides to apply
G. diazotrophicus as a growth promoter, due to the fact
that having a low UPM, considered as the minimum value
at which the farmer can sell the product in the market to
recover the investment (constituting the equilibrium point)
and having a low price, the producer will have more
opportunities to market it, without presenting direct
competition with other producers (Table 3). In this way, the
estimated UPM values that were below US$ 0.14/kg present
an equilibrium point suitable for an adequate profit margin
in the production system. Within this range, the bacterial
suspensions of both strain types with concentrations of
18×107 CFU / mL with and without the nitrogenous and
phosphate fertilization are found. The bacterial suspensions
with concentrations of 8.8×107 CFU/mL presented higher
values in the UPM of US$ 0.17/kg, which is equivalent to
the value perceived in the market for the product, making
these introductions financially unviable (Table 3).
According to the benefit/cost ratio calculated by the
adopted assessment (Table 3), the bacterial suspensions
applied at high concentrations with and without the
nitrogenous and phosphate fertilization showed the highest
profitability along with the control treatment without
fertilization, standing out as financially attractive for an
investor in this type of production system. On the other
hand, the bacterial suspensions applied at low concentra-
tion do not exceed the investors’ perspectives, making the
profitability of the crop unfeasible. For the benefit/cost
ratio, the treatment with the use of the standard strain at a
concentration of d2 without fertilization presented the
highest B/C R (for every dollar invested, the farmer receives
US$ 2.46 gross), followed by the treatments with this same
concentration for the native isolate without fertilization
and the standard strain with nitrogenous and phosphate
fertilization (see Table 3). The lowest relationships were
reported again for the treatments with the isolate GIBI029
at the d1 concentration without and with fertilization (0.27
and 0.29, respectively).
CONCLUSIONS
The use of the diazotrophic bacterium G. diazotrophicus
(standard and native strains) in suspensions with
concentrations of 18×107 CFU/mL in carrot crops makes
possible to significantly improve their economic feasibility,
reaching yields of up to 37,417 kg/ha, even in the case of
no addition of nitrogenous and phosphate fertilizers, as
long as the soil contains the required levels of these
nutrients.
The results obtained in this work indicate that benefit/
cost ratios higher than 1.46 and net income of up to US$
10,817/ha can be achieved. In particular, the possibility of
using the Colombian native isolation GIBI029 of G.
diazotrophicus in an economically efficient way was
demonstrated in the search for more sustainable and
competitive cultural practices.
ACKNOWLEDGEMENTS, FINANCIAL
SUPPORT AND FULL DISCLOSURE
The authors would like to thank the Colombian Ministry
of Science, Technology and Innovation, Minciencias (grant
112752128333), the Vice-Rectorate of Research and
Graduate Studies at the Universidad de Caldas, and the
Table 3: Economic analysis of the carrot crop in the presence of G. diazotrophicus with and without nitrogen and phosphate
fertilization under the conditions of Caldas (Colombia)
Revenue per quality (US$/ha) Revenue (US$/ha)
Extra First Second Third Gross Net
Control-0NP 3,645 1,448 6,967 1,458 579 10,453 6,807 0.13 1.87
Control-100NP 3,961 1,309 4,636 2,813 539 9,297 5,336 0.14 1.35
ATCC-d2-0NP 4,390 7,358 6,377 01,472 15,208 10,817 0.12 2.46
GIBI-d2-0NP 4,072 3,009 2,608 3,210 1,204 10,031 5,959 0.13 1.46
ATCC-d2-100NP 4,335 2,984 2,586 3,183 1,194 9,946 5,611 0.14 1.29
GIBI-d2-100NP 4,385 3,107 2,693 3,314 1,243 10,357 5,972 0.14 1.36
ATCC-d1-0NP 3,715 02,586 3,556 889 7,031 3,316 0.15 0.89
ATCC-d1-100NP 3,998 05,628 1,155 866 7,648 3,650 0.17 0.91
GIBI-d1-0NP 3,424 01,454 895 2,013 4,361 937 0.19 0.27
GIBI-d1-100NP 3,815 01,644 1,012 2,277 4,933 1,118 0.19 0.29
UPM: unit production margin; B/C R: benefit/cost ratio.
Production
costs
(US$/ha)
UPM
(US$/kg)
Treatment B/C R

47
Economic feasibility of Gluconacetobacter diazotrophicus in carrot cultivation
Rev. Ceres, Viçosa, v. 69, n.1, p. 040-047, jan/feb, 2022
Research Direction at the Universidad Católica de
Manizales for funding this work in the framework of the
research project “Production and assessment of a growth
promotor for tomato and carrot crops based on Glucona-
cetobacter diazotrophicus”. The authors declare that they
have no conflict of interest carrying the research and
publishing the manuscript.
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